This invention relates to a double hung or single hung window assembly fabricated or constructed from extrusions of rigid plastics material such as rigid polyvinylchloride, and of the general type disclosed in U.S. Pat. No. 6,055,782 which issued to the assignee of the present invention. In such an assembly, it is desirable for the assembly to withstand high negative windloads which occur, for example, during a hurricane or tornado, and which tend to pull the fabricated sash frame and glass assembly of each window unit out of the fabricated main frame assembly. With such windloads, the lower or bottom horizontal sash rail of the inner or lower window unit is especially subjected to substantial deflection or bowing which can cause damage or breakage to the sash frame and glass assembly of the window unit. When the bottom sash rail of the lower window unit seats within a horizontal channel in the sill member, the channel prevents deflection of the bottom sash rail. However, with a sloping sill member which does not have a channel, there is nothing to resist bending or bowing of the bottom sash rail under such negative pressure.
The present invention is directed to an improved single hung or double hung plastic or vinyl window assembly and which includes a main frame having a pair of vertical jamb members rigidly connected by a horizontal sill member and a horizontal head member and wherein the sloping sill member of the main frame provides for resisting deflection or bowing of the bottom sash rail of the lower window unit. In accordance with one embodiment of the invention, the sill member of the main frame is extruded with an upwardly projecting and horizontally extending integral rib which is located slightly outwardly from a stop or clip member projecting downwardly from the bottom sash rail of the lower window unit. The stop or clip member overlaps the rib which prevents outward bowing or deflection of the bottom sash rail in response to a substantial negative pressure on the window unit.
Other features and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.